Within the overall energy problems facing this country, intense planning is centered around the coal-fired furnaces and oil and gas-fired furnaces which can be retrofitted to burn coal. The coal-fired furnaces utilize a Coutant transition section on the bottom to cool and concentrate the solid residue from the combustion of coal. Essentially, the Coutant transition section is a funnel with sides sloped at 50.degree. to 60.degree. from the horizontal, narrowing to a slot in the order of 2' to 4' wide. Below the slot, a body of water is impounded in the ash hopper which receives the hot, solid fuel residue where it is collected and from which it is subsequently removed.
Although the tubes comprising the water walls are extended down the sides of the Coutant transition section, the volume of the section is below the level of the furnace volume in which the coal is burning and represents a wastage of the combustion chamber volume. The incident radiant heat of the combustion above the section is projected downward into the impounded water below and is not utilized to generate steam.
In retrofitting an oil or gas-fired furnace for burning coal, the inherent losses represented by the Coutant transition section are inherited by the retrofitted furnace. It is desirable in both the originally-designed coal-fired furnace and any retrofitted oil or gas furnaces to reduce the volume of the Coutant transition section to make more efficient use of the combustion chamber volume.
In restatement, currently one of the major problems created when converting large top supported vertical furnace industrial and utility oil and gas-fired boilers to coal, is the tremendous loss in furnace volume that occurs when a conventional Coutant hopper bottom is added for ash removal with coal firing. The reduced furnace volume in this case is generally the limiting factor in determining the maximum boiler capacity in the new coal-firing mode. A structure is desired which will improve the originally designed coal-fired furnaces, as well as the converted oil and gas-fired furnaces, and allow a higher boiler capacity to be obtained when the furnace volume is the limiting factor.
In addition, the structure is expected to be effective in existing ash hoppers to reduce the wasted heat of the incident radiation from the furnace being absorbed by and heating the waste water in the ash hopper. It is sought to significantly reduce, or eliminate, the ash hopper water cooling and recirculation system used to maintain the ash hopper water temperature below the boiling point.